1. Field of the Invention
The disclosure relates to a preparation method of carboxylic acids or ketones using ozone, singlet state-oxygen atom or hydroxyl free radical, and more particularly, to a preparation method of carboxylic acids or ketones using ozone in the dark or under uv light irradiation.
2. Description of the Related Art
As far as plastic industry is concerned, adipic acid and terephthalic acid have been playing critical roles. Adipic acid is a precursor for preparation of nylon; and terephthalic acid can be used to prepare polyethylene terephthalate (PET). In the food processing industry, benzoic acid is served as an additive. Methods for mass production of adipic acid, terephthalic acid and benzoic acid in the current industry are, respectively, to oxidize cyclohexane, p-xylene, and toluene at high temperature and high pressure; and the details can be, respectively, referred to parts (a), (b) and (c) in the Reaction 1.

As shown in part (a) of the Reaction 1, the preparation of adipic acid is by oxidizing cyclohexane using oxygen at a temperature of higher than 125° C. and at a high pressure in the range of 8 to 15 atm in the presence of catalysts, such as, cobalt and manganese, to produce cyclohexanone and cyclohexanol (the so-called “KA” oil), followed by nitric acid (50% to 65%) oxidation to produce adipic acid at temperatures in the range of 70˜90° C. By means of the aforementioned method, the conversion and selectivity are good, though, a side product, N2O, is produced. N2O not only can cause global warming, but also can destruct the ozone layer. Production of 1 kg adipic acid is accompanied with the formation of 0.3 kg of N2O. It is troublesome and energy-consuming to recycle N2O gas, and to avoid direct release to the atmosphere. In addition, the harsh condition of high temperature and high pressure for the Reaction 1 is highly energy-demanding. Moreover, the use of corrosive nitric acid can only be done in expensive titanium reaction vessels, and the operation thereof may be dangerous to the personnel, who is running the reaction.
As shown in the part (b) of the Reaction 1, preparation of terephthalic acid is by oxidizing p-xylene with oxygen at a high temperature of 200° C. and a high pressure of 8 to 15 atm using catalysts, such as, cobalt and manganese along with bromide ions in acetic acid; and the reaction is progressed by multiple steps to produce terephthalic acid. The preparation of terephthalic acid has good conversion and good selectivity. Owing to the high temperature and high pressure, the industrial terephthalic acid production process is also high energy demanding (and thus high production cost). In addition, both bromide ions and acetic acid are corrosive at high temperatures. The primary impurity, 4-carboxybenzaldehyde (4-CBA), is an inhibitor in the latter polyethylene terephthalate (PET) polymerization process, and has to be removed from the terephthalic acid product. Part (c) of the Reaction 1 is akin to the part (b). The preparation of benzoic acid is to oxidize toluene using oxygen (air) at a high temperature and a high pressure in the presence of catalysts, such as, cobalt and manganese along with bromide ions in acetic acid. Consequently, it is also high energy demanding and environmentally unfriendly.
Inasmuch as the preceding technical problems, the scientific community has been seeking for alternatives. In 1994, the preparation of adipic acid by enzymatic catalysis of glucose was reported, and details can be referred to the Reaction 2 below:

As shown in the Reaction 2, the conversion of glucose to adipic acid was achieved in a biochemistry system (enzymes and reagents are not shown), and the yield is up to 97%. Mass production of adipic acid by the above enzymatic process requires the use of million tons of enzymes, which are not commercial available. This method does not comply with efficiency of manufacturing cost. As a result, this enzymatic reaction is still not able to replace the current industrial production of adipic acid.
In addition, another alternative “green” reaction was reported for the preparation of adipic acid via catalytic oxidation of cyclohexene using hydrogen peroxide (H2O2) as an oxidant. The details can be referred to the following Reaction 3.

As shown in the Reaction 3, only H2O2 and water are involved in the reaction, and manufacturing process thereof is very simple and environmentally friendly. However, this cyclohexene-H2O2 process was not industrialized, since the cost of H2O2 is higher than the value of adipic acid produced. Overall, 4-4.4 equivalents of H2O2 was required for production of 1 mole of adipic acid. The price of H2O2 is ˜55% of adipic acid, and thus for the entire reaction, the cost of H2O2 is ˜2.2 times the value of the adipic acid product. Thus, it is economically infeasible. Moreover, cyclohexene is more expensive than cyclohexane. As a result, the reaction is void of industrial applicability.
Because the quantity of the global demand of the adipic acid is ˜3.9 million tons/year in 2014, which is equivalent to a market value of about US$ 6.2 billion. In the case of terephthalic acid, the quantity of worldwide annual production is ˜44 million tons/year in 2014, which is equivalent to a market value of about US$ 44 billion. In the case of benzoic acid, the quantity of worldwide annual production is ˜0.7 million tons/year, which is equivalent to a market value of ˜US$ 1.1 billion. Overall, the total market value of adipic acid, terephthalic acid and benzoic acid is about ˜51.3 billion USD. Hence, if there is a method being able to improve the preceding problems of the three synthesis methods using the same reaction mechanism, it will benefit the industry a lot and reduce the manufacturing cost greatly at the same time.